<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>固定加自适应布局</title>
    <style>
        .box{
            display: flex;
            width: 100%;
            height: 100%;
        }
        .left{
            width: 300px;
            height: 300px;
            background: salmon;
        }
        .right{
            flex: 1;
            background: aqua;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="left"></div>
        <div class="right"></div>
    </div>
</body>
</html>